• Journal of Astronomy and Space Sciences
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• 제27권4호
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• pp.263-278
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• 2010

Many filtered CCD measures form the basis of six new light curves of the eclipsing system SW Lyn. From these measures and additional observations for eclipse timing, 47 new times of minimum light over the time-interval of about 13 years have been calculated. The complex period variability can be sorted into a linear period improvement with 5.8-year and 33.9-year periodic terms. The shorter cyclic term of these is ascribed to a cool companion of the eclipsing pair but the longer one has no testable interpretation at present. The new light curves are synthesized by the 2003 version of the Wilson-Devinney differential corrections computer code. The results incorporate a source of "third light" which comes from the cool companion star that had been identified by the cycling of the period of the eclipsing pair and also had previously been identified spectroscopically. There is a measure of satisfaction with current understanding of the SW Lyn eclipsing system because of consistent syntheses of all historical light curves. This agreeable convergence, however, comes partly at the expense of an unanticipated temperature of the hot star and of a photospheric spot that has no obvious basis in the detached character modeled for the binary. We offer predictions of changes in the stellar parameters if the modeled detached-configuration should be wrong. The SW Lyn stellar system is still difficult to understand.

• 천문학회지
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• 제47권6호
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• pp.259-277
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• 2014

G192.8-1.1 has been known as one of the faintest supernova remnants (SNRs) in the Galax until the radio continuum of G192.8-1.1 is proved to be thermal by Gao et al. (2011). Yet, the nature of G192.8-1.1 has not been fully investigated. Here, we report the possible discovery of faint non-thermal radio continuum components with a spectral index ${\alpha}{\sim}0.56(S_{\nu}{\propto}{\nu}^{-{\alpha}})$ around G192.8-1.1, while of the radio continuum emission is thermal. Also, our Arecibo $H_I$ data reveal an $H_I$ shell, expanding with an expansion velocity of $20-60km\;s^{-1}$, that has an excellent morphological correlation with the radio continuum emission. The estimated physical parameters of the $H_I$ shell and the possible association of non-thermal radio continuum emission with it suggest G192.8-1.1 to be an~0.3 Myr-old SNR. However, the presence of thermal radio continuum implies the presence of early-type stars in the same region. One possibility is that a massive star is ionizing the interior of an old SNR. If it is the case, the electron distribution assumed by the centrally-peaked surface brightness of thermal emission implies that G192.8-1.1 is a "thermal-composite" SNR, rather than a typical shell-type SNR, where the central hot gas that used to be bright in X-rays has cooled down. Therefore, we propose that G192.8-1.1 is an old evolved thermal-composite SNR showing recurring emission in the radio continuum due to a nearby massive star. The infrared image supports that the $H_I$ shell of G192.8-1.1 is currently encountering a nearby star forming region that possibly contains an early type star(s).

• 천문학회지
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• 제37권4호
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• pp.281-284
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• 2004

Optical imaging and spectroscopy of G353.2+0.9, the brightest part of the giant H II region NGC 6357, shows that this H II region is optically thin, contains ${\~}300\;M_{\bigodot}$ of ionized gas and is probably expanding into the surrounding medium. Its chemical composition is similar to that found in other H II regions at similar galactocentric distances if temperature fluctuations are significant. The inner regions are probably made of thin shells and filaments, whereas extended slabs of material, maybe shells seen edge-on, are found in the periphery. The radio continuum and H$\alpha$ emission maps are very similar, indicating that most of the optical nebula is not embedded in the denser regions traced by molecular gas and the presence of IR sources. About $10^{50}$ UV photons per second are required to produce the H$\beta$ flux from the 1l.3'${\times}$10' region surrounding the Pis 24 cluster that is south of G353.2+0.9. Most of the energy powering this region is produced by the 03-7 stars in Pis 24. Most of the 2MASS sources in the field with large infrared excesses are within G353.2+0.9, indicating that the most recent star forming process occured within it. The formation of Pis 24 preceded and caused the formation of this new generation of stars and may be responsible for the present-day morphology of the entire NGC 6357 region.

• 천문학회지
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• 제37권4호
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• pp.285-288
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• 2004

Near-infrared imaging photometry supplemented by optical spectroscopy and narrow-band imaging of the H II region Sh 2-128 and its environment are presented. This region contains a developed H II region and the neighboring compact H II region S 128N associated with a pair of water maser sources. Midway between these, the core of a CO cloud is located. The principal ionizing source of Sh 2-128 is an 07 star close to its center. A new spectroscopic distance of 9.4 kpc is derived, very similar to the kinematic distance to the nebula. This implies a galactocentric distance of 13.5 kpc and z = 550 pc. The region is optically thin with abundances close to those predicted by galactocentric gradients. The $JHK_s$ images show that S 128N contains several infrared point sources and nebular emission knots with large near-infrared excesses. One of the three red Ks knots coincides with the compact H II region. A few of the infrared-excess objects are close to known mid- and far-infrared emission peaks. Star counts in J and $K_s$ show the presence of a small cluster of B-type stars, mainly associated with S 128N. The $JHK_s$ photometric properties together with the characteristics of the other objects in the vicinity suggest that Sh 2-128 and S 128N constitute a single complex formed from the same molecular cloud, with ages ${\~}10^6$ and < $3 {\times} 10^5$ years respectively. No molecular hydrogen emission was detected at 2.12 ${\mu}m$. The origin of this remote star forming region is an open problem.

• 천문학회지
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• 제48권6호
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• pp.333-341
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• 2015

A search for hot and bright white dwarfs (WDs) in the Milky Way globular clusters M13 (NGC 6205) and M22 (NGC 6656) is carried out using the deep and homogeneous V I photometric catalog of Anderson et al. and and Sarajedini et al., based on data taken with the ACS/WFC aboard the Hubble Space Telescope (HST). V versus V − I color-magnitude diagrams (CMDs) of M13 and M22 are constructed and numerous spurious detections are rejected according to their photometric quality parameters qfit(V ) and qfit(I). In the case of M13, further radial restriction is applied to reject central stars with higher photometric errors due to central crowding. From each resultant V versus V −I CMD, sixteen and thirteen WD candidates are identified in M13 and M22, respectively. They are identified as stellar objects in the accompanying ACS/WFC images and are found to be randomly distributed across the central regions of M13 and M22. Their positions in the CMDs are in the bright part of the DA WD cooling sequences indicating that they are true WDs. In order to confirm their nature, follow-up spectroscopic observations are needed.

• 천문학회지
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• 제48권6호
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• pp.343-355
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• 2015

There is much observational evidence that active star formation is taking place in the Hii regions Sh 2-255 – 257. We present a photometric study of this star forming region (SFR) using imaging data obtained in passbands from the optical to the mid-infrared, in order to study the star formation process. A total of 218 members were identified using various selection criteria based on their observational properties. The SFR is reddened by at least E(B −V ) = 0.8 mag, and the reddening law toward the region is normal (R_V = 3.1). From the zero-age main sequence fitting method it is confirmed that the SFR is 2.1 ± 0.3 kpc from the Sun. The median age of the identified members is estimated to be about 1.3 Myr from a comparison of the Hertzsprung-Russell diagram (HRD) with stellar evolutionary models. The initial mass function (IMF) is derived from the HRD and the near-infrared (J, J −H) color-magnitude diagram. The slope of the IMF is about Γ = −1.6 ± 0.1, which is slightly steeper than that of the Salpeter/Kroupa IMF. It implies that low-mass star formation is dominant in the SFR. The sum of the masses of all the identified members provides the lower limit of the cluster mass (169M_⊙). We also analyzed the spectral energy distribution (SED) of pre-main sequence stars using the SED fitting tool of Robitaille et al., and confirm that there is a significant discrepancy between stellar mass and age obtained from two different methods based on the SED fitting tool and the HRD.

• 천문학논총
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• 제30권2호
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• pp.265-266
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• 2015

A search for luminous white dwarfs (WDs) in several nearby Galactic globular clusters (GCs) was carried out using the deep and homogeneous photometric catalog of Galactic GCs taken with the ACS/WFC aboard the Hubble Space Telescope (HST) by Sarajedini et al. and Anderson et al- It resulted in the identification of luminous WD candidates in the GCs M13 (NGC 6205) and M22 (NGC 6656). The purpose of the present study is to identify luminous WDs in the deep and homogeneous V versus V - I color-magnitude diagrams (CMDs) of several nearby Galactic GCs taken with the ACS/WFC aboard the HST. Using photometric data for the GCs M13 and M22 that are now in the public domain, the V versus V - I CMDs of the GCs M13 and M22 were constructed. Many spurious detections in the CMDs were removed using the photometric quality parameters qfit(V) and qfit(I), and a radial restriction was applied to the CMDs to remove the central stars with higher photometric errors due to central crowding. From each resultant V versus V - I CMD of the GCs M13 and M22, a dozen or so luminous WD candidates were identified. They were confirmed as stellar objects in the accompanying ACS/WFC images and their positions in the CMDs were in the bright part of the DA WD cooling curve. Therefore, the luminous WD candidates in the GCs M13 and M22 seem to be true luminous WDs, and spectroscopic observations are needed to confirm their true identity.

• 한국융합학회논문지
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• 제11권6호
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• pp.259-268
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• 2020

본 연구는 팬덤활동에 연구들을 총체적·계량적으로 분석한 후 팬덤활동의 구성 유형과 효과를 검증하는 데 목적이 있다. 연구결과는 다음과 같다. 효과크기 비교 시 사회경제분야 관련 변인이 가장 큰 효과크기를 보였고, 다음은 개인 행동, 개인심리로 효과크기가 나타났다. 다음으로 팬덤활동의 영향요인에서 긍정적 변인의 효과크기가 중간 수준의 효과크기를 나타내고 부정적 변인의 효과크기가 낮은 수준의 효과크기를 보이는 것으로 나타났다. 또한 팬덤 형태 내 분석에서는 팬덤이 아이돌 팬덤일 때 가장 효과크기가 크고, 그다음은 스포츠스타, 배우 순이었다. 연구 대상자 중 효과크기는 대학생, 전체, 성인, 중고등학생, 중학생 순으로 나타났다. 한편 나라별 구분에 따른 분석을 실시한 결과 중국이 가장 효과크기가 높고, 유사하게 미국의 경우도 높은 수준의 효과크기가 있었다. 반면 대한민국의 경우 효과크기가 나타나 낮은 수준의 효과크기를 보였다.

• 천문학회지
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• 제38권2호
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• pp.279-282
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• 2005

We report the millimeter-wave radio observations of molecular cloud cores in Taurus. The observed line is the $N_2H^+$ emission at 93 GHz, which is known to be less affected by molecular depletion. We have compared starless (IRAS-less) cores with star-forming cores. We found that there is no large difference between starless and star-forming cores, in core radius, linewidth, core mass, and radial intensity profile. Our result is in contrast with the result obtained by using a popular molecular line, in which starless cores are larger and less condensed. We suggest that different results mainly come from whether the employed molecular line is affected by depletion or not. We made a virial analysis, and found that both starless and star-forming cores are not far from the critical equilibrium state, in Taurus. Together with the fact that Taurus cores are almost thermally supported, we conclude that starless Taurus cores evolve to star formation without dissipating turbulence. The critical equilibrium state in the virial analysis corresponds to the critical Bonnor-Ebert sphere in the Bonnor-Ebert analysis (Nakano 1998). It is suggested that the initial condition of the molecular cloud cores/globules for star formation is close to the critical equilibrium state/critical Bonnor-Ebert sphere, in the low-mass star forming region.

• 천문학회지
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• 제34권3호
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• pp.157-166
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• 2001

The molecular cloud associated with the H II region S301 has been mapped in the J = 1-0 transitions of $^{12}CO$ and $^{13}CO$ using the 13.7 m radio telescope of Taeduk Radio Astronomy Observatory. The cloud is elongated along the north-south direction with two strong emission components facing the H II region. Its total mass is $8.7 {\times} 10^3 M{\bigodot}$. We find a velocity gradient of the molecular gas near the interface with the optical H II region, which may be a signature of interaction between the molecular cloud and the H II region. Spectra of CO, CS, and HCO+ exhibit line splitting even in the densest part of the cloud and suggests the clumpy structure. The radio continuum maps show that the ionzed gas is distributed with some asymmetry and the eastern part of the H II region is obscured by the molecular cloud. We propose that the S301 H II region is at the late stage of the champagne phase, but the second generation of stars has not yet been formed in the postshock layer.